Ergonomically friendly orbital sander construction

ABSTRACT

A random orbital sander including a housing, a motor having a vertical axis in the housing, a pad coupled to the motor, a face on the pad extending substantially perpendicularly to the vertical axis, a shroud surrounding the pad, an opening in the shroud, and a dust discharge tube having an inner end in communication with the opening and an outer end on the dust discharge tube end extending at an acute angle to the face of the pad. An orbital sander wherein the pad is supported from the sander housing by columnar units located on opposite sides of the motor. A bore in the motor shaft conducts compressed air through the chamber housing the bearings which support the spindle which mounts the pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of applicationSer. No. 09/408,192, filed Sep. 29, 1999, which is acontinuation-in-part of application Ser. No. 08/787,873, filed Jan. 23,1997, now U.S. Pat. No. 6,004,197.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] The present invention relates to an improved ergonomicallyfriendly surface-treating tool in which a flat surface of a pad engagesthe surface of a workpiece for the purpose of abrading or polishing itand more particularly to an improved orbital sander.

[0004] By way of background, in operation, orbital sanders create forcesat the sanding surface which are transmitted back to the operator's handand arm through a lever which is the height of the orbital sanderbetween the face of the sanding disc and the top of the casing at thevertical centerline of the sander. Therefore, if this height is as shortas possible, the operator's effort in overcoming the forces produced atthe face of the sanding disc are less than if the height was greater.

[0005] In orbital sanders it is desirable that, in addition for theheight of the tool being as small as possible, the connection betweenthe housing and the pad should be sufficiently flexible to permit goodorbital action but it should also provide good columnar strength so thatthe pad will oscillate in a very close plane, that is, movement in avertical direction should be limited as much as possible.

[0006] In prior orbital sanders there were various types of connectionsbetween the housing and pad. In one type, a central relatively softrubber post connected the pad to the housing. While this providedsufficient orbital flexibility, it permitted the pad to move out of adesired plane. In another type, thin rigid plastic multi-columnar postunits were located at the corners of the pad between the pad and thehousing. These thin rigid post units provided good columnar stability soas to confine the pad to a desired plane, but they had to be relativelylong so as to be sufficiently flexible laterally to provide good orbitalaction, thereby increasing the height of the sander.

[0007] In addition, in all prior orbital sanders, the abrasive dustenters the housing containing bearings which support the spindle whichcarries the pad, thereby shortening the bearing life and also causingthe pad to operate out of its desired plane. This is especiallypronounced in the type of orbital sanders using central vacuum systemswherein a high volume of air is drawn through the sander housing tocarry away the abrasives and foreign particles. This causes eddycurrents at the various sharp edges including the edges of the eccentrichousing which contains the bearings which mount the spindle to which thepad is attached. Abrasives and foreign particles may thus enter thebearing area because they are sucked in to this area because of changesin positive and negative pressures due to the operation of the tool. Oneattempt to reduce the amount of foreign matter entering the bearing areais shown in U.S. Pat. No. 4,854,085 which utilized a triple seal. Thisapproach did increase the bearing life to a certain degree. It is withovercoming the foregoing deficiencies of the prior art that the presentinvention is concerned.

BRIEF SUMMARY OF THE INVENTION

[0008] It is one object of the present invention to provide an improvedorbital sander which has a relatively low height which contributestoward making the sander ergonomically friendly and which has goodcolumnar strength between the housing and the pad so as to tend toconfine the pad to an orbital plane while providing sufficient lateralflexibility for good orbital action.

[0009] Another object of the present invention is to provide an uniquemounting between the housing and pad of an orbital sander which providesgood lateral flexibility of the pad while tending to confine it to anorbital plane of operation.

[0010] A further object of the present invention is to provide animproved structural arrangement for essentially preventing foreignmatter from entering the eccentric housing containing the spindlebearings of an orbital sander, thus prolonging the life of the bearingsto a much greater extent than was heretofore possible by the use ofprior types of seals. Other objects and attendant advantages of thepresent invention will readily be perceived hereafter.

[0011] The present invention relates to an orbital sander comprising ahousing, a compressed air motor in said housing, a pad support securedto said motor, and first and second elongated rows of spaced plasticcolumns located on opposite sides of said motor and located between saidhousing and said pad support.

[0012] The present invention also relates to an orbital sander as setforth in the preceding paragraph including a shaft in said motor, arotor mounted on said shaft, a compressed air duct in said motor forconducting compressed air to said rotor, an eccentric housing mounted onsaid shaft, a chamber in said eccentric housing, at least one bearing insaid eccentric housing, said pad support being secured to said eccentrichousing, and means in said motor for conducting compressed air to saidchamber.

[0013] The present invention also relates to a plastic columnar unit foran orbital sander comprising an upper bar member, a lower bar member,and a row of a plurality of spaced columns between said upper and lowerbar members.

[0014] The various aspects of the present invention will be more fullyunderstood when the following portions of the specification are read inconjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0015]FIG. 1 is a fragmentary plan view of a central vacuum orbitalsander with the vacuum hose and the compressed air hose connected to theorbital sander;

[0016]FIG. 1A is an enlarged fragmentary cross sectional view takensubstantially along line 1A-1A of FIG. 1;

[0017]FIG. 1B is a cross sectional view taken substantially along line1B-1B of FIG. 1A;

[0018]FIG. 1C is a cross sectional view taken substantially along line1C-1C of FIG. 1A;

[0019]FIG. 1D is a cross sectional view taken substantially along line1D-1D of FIG. 1A;

[0020]FIG. 1E is a cross sectional view taken substantially along line1E-1E of FIG. 1A;

[0021]FIG. 1F is a cross sectional view taken substantially along line1F-1F of FIG. 1A;

[0022]FIG. 2 is a fragmentary side elevational view of the orbitalsander of FIG. 1;

[0023]FIG. 2A is a fragmentary cross sectional view taken substantiallyalong line 2A-2A of FIG. 2 and showing the support structure for thedust discharge tube;

[0024]FIG. 2B is a fragmentary extension of the top of the structureshown in FIG. 2A;

[0025]FIG. 3 is a fragmentary view, partially in cross section, takensubstantially along line 3-3 of FIG. 1, and showing the relationshipbetween the shroud and the dust discharge tube and the discharge hose;and also showing the relationship between the motor exhaust tube and thedust discharge tube;

[0026]FIG. 4 is a fragmentary plan view of a self-generated vacuumorbital sander with the vacuum hose and the compressed air hoseconnected to the orbital sander and to each other;

[0027]FIG. 5 is a fragmentary side elevational view of the sander ofFIG. 4;

[0028]FIG. 6 is an enlarged fragmentary cross sectional view takensubstantially along line 6-6 of FIG. 5 and showing the structure of themotor exhaust tube, the dust discharge tube containing an aspirator, theconnection therebetween and the connection between the dust dischargetube and the flexible hose;

[0029]FIG. 6A is a cross sectional view taken substantially along line6A-6A of FIG. 6;

[0030]FIG. 7 is a fragmentary enlarged cross sectional view takensubstantially along line 7-7 of FIG. 4 and showing the compressed airvalve inlet structure;

[0031]FIG. 8 is a fragmentary cross sectional view taken substantiallyalong line 8-8 of FIG. 7 and showing the compressed air flow adjustingvalve in a full open position;

[0032]FIG. 9 is a view similar to FIG. 8 but showing the valve in apartially open position;

[0033]FIG. 10 is a view similar to FIG. 8 and showing the valve in afully closed position;

[0034]FIG. 11 is an enlarged fragmentary enlarged cross sectional viewsimilar to FIG. 7 but showing the compressed air inlet valve in an openposition;

[0035]FIG. 11A is an enlarged perspective view of the compressed airflow control valve;

[0036]FIG. 11B is a side elevational view of the compressed air flowcontrol valve;

[0037]FIG. 12 is a fragmentary cross sectional view taken substantiallyalong line 12-12 of FIG. 11 and showing the relationship between theposition between the compressed air inlet valve and the air flowadjusting valve when the latter is in a fully open position;

[0038]FIG. 13 is a view similar to FIG. 12 but showing the relationshipwhen the air flow adjusting valve is in a partially open position;

[0039]FIG. 14 is a view similar to FIG. 12 but showing the relationshipwhen the air flow adjusting valve is in a closed position;

[0040]FIG. 15 is a side elevational view of a central vacuum typeorbital sander showing the various dimensions which are considered indetermining ergonomics;

[0041]FIG. 16 is a side elevational view of a self-generated vacuum typeof orbital sander showing the various dimensions which are considered indetermining ergonomics;

[0042]FIG. 17 is a cross sectional view taken substantially along line17-17 of FIG. 1F and showing a modification of the rotor shaft forpositively pressurizing the bearings in the eccentric housing;

[0043]FIG. 18 is an exploded view of the rotor shaft and relatedstructure of FIG. 17;

[0044]FIG. 19 is a modified form of FIG. 1A showing another embodimentfor conducting compressed air to the bearings in the eccentric housing;

[0045]FIG. 20 is a view similar to FIG. 19 and showing a duct in theform of a slot in the rotor shaft for conducting compressed air to thebearings in the eccentric housing;

[0046]FIG. 21 is a view similar to FIG. 19 and showing anotherembodiment of a duct which includes an inclined duct or bore in therotor shaft for conducting compressed air to the bearings in theeccentric housing;

[0047]FIG. 22 is a perspective view of the improved orbital sander ofthe present invention having the unique columnar mounting units betweenthe housing and the pad;

[0048]FIG. 23 is a cross sectional view taken substantially along line23-23 of FIG. 22;

[0049]FIG. 24 is a cross sectional view taken substantially along line24-24 of FIG. 23;

[0050]FIG. 25 is an exploded view of the orbital sander of FIGS. 22-24;

[0051]FIG. 26 is an enlarged exploded view of a portion of FIG. 25showing the lower housing section and the columnar units which join thepad to the housing sections;

[0052]FIG. 27 is a fragmentary perspective view showing the lowerhousing sections assembled with the columnar units;

[0053]FIG. 28 is a cross sectional view taken substantially along line28-28 of FIG. 27;

[0054]FIG. 29 is a cross sectional view of the columnar unit takensubstantially along line 29-29 of FIG. 26;

[0055]FIG. 29A is a view showing the preferred structure of a column ofthe columnar unit;

[0056]FIG. 30 is a cross sectional view taken substantially along line30-30 of FIG. 29; and

[0057]FIG. 31 is a cross sectional view taken substantially along line31-31 of FIG. 29.

DETAILED DESCRIPTION OF THE INVENTION

[0058] The present invention relates to an orbital sander which has arelatively low height and thus is ergonomically friendly, while alsoproviding good columnar strength to maintain the pad in a close orbitalplane and also permitting good orbital flexibility. Its low height isdue in part to the compressed air motor which drives it, and this motoris the same that is used in the three previous types of random orbitalsanders which are described hereafter. Its low height is also due to theuse of a columnar connection between the housing in the pad whichprovides good columnar strength while providing good orbitalflexibility.

[0059] The compressed air motor which is used in the orbital sander ofthe present invention is also used in the three basic types of randomorbital sanders which are described hereafter. The first and mostrudimentary type is the non-vacuum type which does not have any vacuumassociated with it for the purpose of conveying away the dust which isgenerated during a sanding operation. The second type is the centralvacuum type which has a vacuum hose attached at one end to a centralvacuum source and at its other end to a fitting which is incommunication with the shroud of the sander so as to create a suctionwhich carries away the dust which is generated during a sandingoperation. The third type is a self-generated vacuum type wherein theexhaust air from the air motor is associated with an aspirator incommunication with the shroud for carrying away the dust which isgenerated during a sanding operation. While not specifically shown inthe orbital sander of the present invention of FIGS. 22-31, it will beappreciated that the above features of the central vacuum type andself-generated vacuum type may be incorporated therein.

[0060] Summarizing in advance, the orbital sander of the presentinvention shown in FIGS. 22-31 includes the compressed air motor of theforegoing type of sanders which, in part, permits the sander of thepresent invention to have a relatively low height, which thus reducesstresses experienced by the operator. However, it will be appreciatedthat the elongated rows of spaced plastic columns which secure the padplate to the housing in FIGS. 22-31 may be used with other motors whichdo not have the low height of the motor described hereafter.

[0061] In FIGS. 1, 1A, 2, 2A, 2B and 3 a central vacuum type of randomorbital sander 10 is disclosed wherein a flexible vacuum hose 11 isconnected between the dust discharge tube 12 and the shroud 13 whichsurrounds the sanding disc 14. However, the only difference between thecentral vacuum type orbital sander 10 and a non-vacuum type is that thelatter does not have the dust discharge tube 12 or the flexible hose 11.The basic structure which is common to all three types of orbitalsanders is shown in FIG. 1A which is taken along line 1A-1A of FIG. 1.The sander of the foregoing figures is being described hereafter for thepurpose of setting forth the structure of the compressed air motor usedin the orbital sander of the present invention shown in FIGS. 22 et seq.which contributes in part to the low height of the sander of the presentinvention.

[0062] The basic construction of the random orbital sander of FIGS. 1-3includes a housing grip 15 of a rubber type material which is mounted onplastic housing 17 and secured thereon by coacting with ribs 19, 20 and21 which extend partially around housing 17. Housing 17 also includes alower portion 22 which terminates at a skirt 23 having an annular rib24′ thereon onto which flexible plastic shroud 13 is mounted with a snapfit.

[0063] An air motor is located within housing 17, and it includes acylinder 24 in which a rotor 25 keyed to shaft 27 by key 28 is mounted.The ends of shaft 27 are mounted in bearings 29 and 30 (FIG. 1A), and asnap ring 31 retains shaft 27 in position. The cylinder 24 is part of acylinder assembly which includes an upper plate 32 and a lower plate 33.The bearing 29 is mounted into annular portion 63 of upper plate 32, andthe bearing 30 is mounted into annular portion 28 of lower plate 33. Theend plates 32 and 33 include planar surfaces 34 and 35, respectively,which bear against the ends of cylinder 24 to thereby provide therequired sealing with the adjacent portions of the cylinder 24. A pin 37has an upper end which is received in a bore 39 in housing 17. Pin 37passes through a circular bore 40 in end plate 32 and through a bore 41in cylinder 24 and into a bore 42 in end plate 33, thereby aligning theend plates 32 an 33 with the cylinder 24. The outer circular ends 43 and44 of end plates 32 and 33, respectively, have a tight fit with theinternal surface 45 of housing 17. A threaded lock ring 47 is threadedinto tapped portion 49 of housing 17 to thus cause the upper surface 50of end plate 32 to bear against the adjacent surface of housing 17. AnO-ring 51 in a groove in lock ring 47 bears against the undersurface 52of lower end plate 33. Rotor shaft 27 has an eccentric housing 57 formedintegrally therewith into which bearings 55 are mounted and retainedtherein by snap ring 56 which bears on Belleville washer 58. Housing 57is an eccentric having two counter-weights 54 and 57′. A stub shaft 53is press-fitted into bearings 55 and it is formed into a nut 59 at itsouter end. Thus, rotor shaft 27 will rotate and eccentric housing 57will simultaneously rotate with shaft 27. A threaded shaft 60 extendsupwardly from sanding disc 14 and is received in stub shaft 53.

[0064] As can be seen from FIGS. 1A and 1F a compressed air inletconduit 38 is in communication with bore 134 in cylinder 24, and bore134 is in communication with bore 134′ which extends axially betweenupper cylinder surface 50 (FIG. 1D) and lower cylinder surface 35 (FIG.1A). Bore 134′ is in communication with groove 136 (FIG. 1D) in uppercylinder surface 50 and a like groove (not shown) in lower cylindersurface 35. When upper plate 32 is in assembled position, it causesgroove 136 to be a conduit leading to chamber 138 (FIG. 1D) withincylinder 24. Lower plate 33 forms a similar conduit with the groovewhich corresponds to groove 136 in lower cylinder surface 35. Aplurality of vanes 136′ (FIG. 1D) are slidably mounted in radial slots139′ in plastic rotor 25 and their outer ends contact the inner surfaceof cylinder 24 because they are forced outwardly by air pressure whichis conducted to the inner ends of slots 139′ by groove 140′ (FIG. 1B) inthe surface 64 of plate 32. Groove 140′ is in communication with groove136. Lower plate 33 (FIG. 1C) has a groove 141′ which corresponds togroove 140′ and is in communication with a groove which corresponds togroove 136. Air is exhausted from chamber 142′ of cylinder throughnarrow slots 143′ (FIG. 1F) a few millimeters wide in the centralportion of cylinder 24, and this exhaust air passes into chamber 144′between cylinder 24 and housing 17, and it thereafter passes throughbore 142 (FIGS. 1F and 3) into exhaust conduit 87.

[0065] At this point it is to be noted that the air motor is of aconventional type which has been constructed for causing the overallheight of the above-described unit in FIG. 5 to be lower than existingorbital sanders having a similar construction and for causing it to havea lower weight.

[0066] The modifications which have been made are as follows: The top 60of housing 17 is 2.0 millimeters thick. Additionally, the clearance at61 between the inner surface 62 of housing 17 and the edge 63 is 0.6millimeters. In addition, the thickness of end plate 32 between surface50 and surface 64 is 2.5 millimeters, and the thickness of end plate 33between surface 35 and surface 67 is 2.5 millimeters. The cylinder 24′has an axial length of 20 millimeters. In addition, the clearance 69 is0.5 millimeters. Also, nut 59 is 4.0 millimeters thick. The eccentrichas a height of 21.4 millimeters. All of the foregoing dimensions havecaused the air motor to have a height of 82.92 millimeters from the topof housing 17 to the face 70 of pad 14 at the vertical centerline 71.This compares to the lowest known existing prior art structure which hasa height of approximately 89 millimeters to thereby reflect a differenceof 6.08 millimeters or approximately 7%. In addition, the use ofaluminum end plates 32 and 33, rather than steel, plus having the outersurface 72 of cylinder 24 to be 2 millimeters and the absence of anupper flange which corresponds to flange 73 and the thinning of aluminumend plate 33 and the thinning of nut 59 reduces the weight of theorbital sander of FIG. 5 to 0.68 kilograms as compared to a similarprior art sander which has a weight of 0.82 kilograms, therebyreflecting a difference of approximately 0.14 kilograms or about 17%. Asnoted above, the lesser weight makes it easier for a person to handlethe orbital sander.

[0067] As noted above, the basic structure of the air motor is a wellknown conventional type having 150 watts minimum power at 0.61 bar airpressure minimum. The above features of the presently described airmotor cause the orbital sander of FIGS. 1-21 to be of a relatively lowheight and a relatively low weight. Otherwise, the internals of the airmotor are conventional.

[0068] The reduced height of sander 10 is depicted by letter A in FIG.15. The fact that the entire height of sander 10 is lower, results inthe lowering of the centerline of the outlet of the dust discharge tubeto a dimension B and also results in the lowering of the centerline ofthe compressed air inlet 80 to a dimension C. As noted above, thelowering of dimensions B and C also results in enhancing the ease ofhandling of the orbital sander 10.

[0069] The dust discharge tube 12 (FIG. 3) of sander 10 has a centerline86 and is inclined to the horizontal at an angle a. The dust dischargetube 12 consist of a longer section 83 and a shorter section 84 whichhas a centerline 88 and which has a circular outlet which mounts oncylindrical stub pipe 85 formed integrally with shroud 13. The dustdischarge tube portion 83 is located immediately below the motor exhaustinlet fitting 87. The air motor exhaust conduit 87 is within housingportion 90 which is molded integrally with housing 17. Housing portion90 also contains compressed air inlet conduit 80 (FIGS. 1 and 2A). Thedust discharge tube 12 is also attached to housing portion 90 by a bolt91 which extend through horizontal portion 92 of unit 90 and alsoextends through web 93 which spans legs 94 and 95 molded integrally withdust discharge tube 12. Thus, dust discharge tube 12 is firmly supportedon stub tube 85 and on housing portion 90 which contains the air motorexhaust conduit 87 and the compressed air inlet 80.

[0070] As noted briefly above, since the outer end portion 89 (FIG. 3)of dust discharge tube 12 is inclined upwardly, the adjacent portion offlexible vacuum hose 11 will also be inclined upwardly to thus cause itto droop further away from the outlet 89 then if the latter washorizontal. This tends to lessen the possibility that the flexible hosewill contact the workpiece which could create a frictional drag. Inaddition, as can be seen from FIG. 2, since the flexible hose 11 isreceived directly in dust discharge tube 12, a fitting which isotherwise used at the outer end of a dust discharge tube in the priorart is eliminated which thus causes the extreme outer end 81 ofdischarge tube 12 to be at a distance E (FIG. 15) from the verticalcenterline 71 of the sander. It will be appreciated that the shorterthat the distance E is, the shorter is the lever arm tending to tilt thesander 10 and thus for any given weight at the outer end 81 of dustdischarge tube 12, the shorter the lever arm E is, the lower will be thetilting force which is produced and the lower will be the force requiredby the operator to overcome this tilting force.

[0071] The compressed air inlet structure permits a very gradual varyingof the pressure which is supplied to the air motor. In this respect, thecompressed air inlet 80 includes a valve 100 (FIG. 1A) which is biasedagainst seat 101 by spring 102 which has its outer end 103 bearingagainst the end of hollow compressed air fitting 104 which is threadedinto housing portion 90. Fitting 104 (FIGS. 1, 2, 4 and 5) receives theend of compressed air hose 106 with a conventional connection. Hose 106is attached to vacuum hose 11 by strap 108. In order to open valve 100from the position shown in FIGS. 1A and 7 to the position shown in FIG.11, lever 105 is pivotally mounted at 107 on boss 109 which is moldedintegrally with housing portion 90. When lever 105 is depressed, it willdepress pin 110 from the position shown in FIG. 7 to the position shownin FIG. 9 against the bias of spring 102 in view of the fact that theextension 111 of valve 100 is received in a bore 112 at the lower end ofpin 110. When lever 105 is released, the spring 102 will return valve100 to the position of FIG. 7 and pin 110 will be raised to the positionof FIG. 7 by virtue of its connection with valve extension 111. Theforegoing structure of valve 100 is conventional.

[0072] A flow adjusting valve 115 (FIGS. 1A, 7, 11A and 11B) is locatedin bore 117 of housing portion 90 and it is retained therein by snapring 119 (FIG. 7). Bore 117 has a wall 118. An O-ring 120 is mounted ina groove 122 of base 126 of valve body 121 (FIG. 11A). O-ring 120performs both a sealing function and a frictional holding function toretain valve 115 in any adjusted position in bore 117. The valveconsists of a portion 123 of a cylinder extending upwardly from base 126and having an outer cylindrical surface 124. A handle 125 is moldedintegrally with valve body 121. The upstanding wall 123 includes anaperture 127 and an inclined groove 129 in communication with bore 127.The outer surface 124 is in sliding contact with wall 130 of bore 117.When valve 121 is in a fully open position shown in FIG. 8, bore 127 isin communication with bore 38 (FIG. 1A) of housing 17. Bore 38terminates at wall 132 of air motor cylinder 25. An O-ring 133 isinserted in wall 132 (FIG. 1F) around bore 134 which provides a sealwith the outer end of conduit 38. The foregoing structure is well knownin the art.

[0073] As noted above, valve 115 is fully open in the position shown inFIG. 8. In FIG. 9 it is partially open and it can thus be seen that theair flow must pass along inclined groove 129 which restricts the openingto conduit 38. It will be appreciated that the more that wall 121 ismoved in a counterclockwise direction, the smaller will be the path ofcommunication leading to duct 38. In FIG. 10 the valve is shown in afully closed position wherein the wall 124 completely closes off duct38. At this time the edge 135 engages shoulder 137 to define the limitof counterclockwise movement of valve 115, as shown in FIG. 10. Theclockwise limit of movement of wall 124 is determined when edge 139engages shoulder 140, as shown in FIG. 10. The range of movement ofvalve 125 is 90° from a full open position to a full closed position.

[0074]FIGS. 12, 13 and 14 correspond to FIGS. 8, 9 and 10, respectively,but are taken along cross section line 12-12 above valve extension 111whereas FIGS. 8, 9 and 10 are taken through valve extension 111 in FIG.7.

[0075] In FIG. 3 motor air exhaust housing 87 is shown which is incommunication with the exhaust of air motor cylinder 24 (FIG. 1A)through conduit 142 (FIG. 3). Housing 90 includes a muffler 143 which isheld in position in bore 144 by plug 145 and the exhaust air exitshousing 90 through perforated cap 147.

[0076] In FIGS. 4, 5, 6 and 7 a self-generated vacuum random orbitalsander 150 is shown. This sander has the same internal structuredescribed above relative to the central vacuum type, as shown in FIG.1A. In addition, it has the same type of sanding pad 14 and it has thesame type of valve 115 described above which is located in housing unit90. The inlet valve 115 is identical to valve 125 described above inFIGS. 1A, 8, 9 and 10.

[0077] The self-generated vacuum random orbital sander 150 includes adust discharge tube 151 which is also inclined to the horizontal at anangle a (FIG. 5). Dust discharge tube 151 includes an elongated portion152 which has a centerline 156 (FIG. 16) and is received in elbow 153which has a centerline 158 and which in turn is mounted on stub pipe 154of shroud 13. A tubular strap portion 155 is formed integrally withportion 156. Motor exhaust unit 159 contains a porous muffler 160. Afitting 161 extends through strap 155 and is threaded into motor exhausthousing 159 at 162 and it includes a bore 163 and a plurality ofapertures leading from bore 163 to conduit 165 which is the entryportion of bore 167 which functions as an aspirator 176 in conjunctionwith the areas 169 and 170 of elongated dust discharge tube portion 150.It is to be especially noted that the dust discharge from shroud 13enters the straight portion of dust discharge tube 152 and the fact thatthere is no sharp bend in the immediate vicinity of areas 171 and 169,there will be greater efficiency than if such a bend existed immediatelyadjacent to conduit 165.

[0078] In addition to the foregoing, the flexible dust discharge hose 11is received in the enlarged portion 172 at the outer end of dustdischarge tube 151 in the same manner as described above relative to theembodiment of FIGS. 1-3. The outer portion 170 of aspirator 176 isnested within the innermost portion of dust discharge hose 11 (FIG. 6),thereby contributing to the overall relative shortness of dust dischargetube 151.

[0079] It is to be noted that the dust discharge tube 151 is inclined atan angle a to the horizontal and that elbow 153 is inclined at an angleb to the horizontal.

[0080] It is to be further noted from FIG. 16 that the centerline ofdust discharge tube 151 at the outer end of portion 172 is a distance Efrom the vertical centerline 71 of the random orbital sander 150. Dustdischarge tube 151, in addition to being inclined, is relatively shortso that any downward force at its outer end will be relatively close tothe vertical centerline 71 and will therefore create less of a forcewhich the operator must oppose than if it were longer.

[0081] The following table sets forth the dimensions A through E andangles a and b shown in FIGS. 15 and 16. TABLE DIMENSIONS IN MILLIMETERSOF VARIOUS PORTIONS OF DIFFERENT TYPES OF ORBITAL SANDERS SELF-GENERATEDCENTRAL NON-VACUUM VACUUM VACUUM A 82.92 82.92 82.92 B — 47.45 40.42 C58.42 58.42 58.42 D 80.00 80.00 80.00 E — 147.28  130.05  Angle a —  10° 10° Angle b — 130° 130°

[0082] In the above table, the dimension E is 130.05 millimeters for thecentral vacuum sander and 147.28 millimeters for the self-generatedvacuum sander. However, if the threaded connection at outer end portion89 (FIG. 3) of dust discharge tube 12 of the central vacuum sander isdecreased by two threads at 5 millimeters each, then the 130.05dimension E would be decreased about 10 millimeters to about 120millimeters. Also, if the threaded end portion 172 of the self-generatedvacuum sander is decreased by two threads at 5 millimeters each, the147.28 dimension E would be decreased 10 millimeters to about 137millimeters. It is possible with a slight loss of ergonomics to lengthenthe dimension E for the central vacuum and self generated vacuum sandersby about 10 millimeters to about 140 millimeters and about 157millimeters, respectively. However, when the foregoing lengtheneddimensions E are considered in combination with the lower heightdimension A, each of the foregoing sanders will still be moreergonomically friendly than sanders not having this combination ofdimensions.

[0083] As noted briefly above, the closest known prior art sander of theabove-described type shown in FIGS. 1-21 has a height dimension ofapproximately 89 millimeters as compared to height dimension A of 82.92millimeters of the above-described sander. As further noted above thereis a difference of about 7% between the two dimensions. The 82.92millimeter dimension is the ultimate low dimension which was able to beachieved while still retaining the various component parts of the sanderin a commercially operable manner for providing the desired outputparameters noted above and also recited hereafter. However, it will beappreciated that the height dimension A of the present sander can beincreased a few millimeters by not reducing the thickness and height ofthe various components as much as was done. Accordingly, it iscontemplated that the height dimension A can be increased to 86millimeters which would still be a reduction in height from 89millimeters or approximately 3.5%.

[0084] Additionally, as noted above the closest known prior art sanderof the present type has a weight of 0.82 kilograms as compared to theweight of the present sander of 0.68 kilograms, or a difference of 0.14kilograms or a weight reduction of approximately 17%. It will beappreciated that the weight of the sander of the present invention maybe increased to 0.75 kilograms which would be a difference ofapproximately 0.07 kilograms, and this would be a weight reduction ofapproximately 8.3% which also could be significant.

[0085] The preferred angle a shown above in the table is an acute angleof 10°. However, this angle may be as small as about 5° and as high asabout 30°. The exact acute angle for any specific device will depend onvarious factors such as the length of the motor exhaust body which islocated directly above it and the vertical spacing between the shroudoutlet and the motor exhaust body.

[0086] As noted above, the angle b is 130°, but it can be any obtuseangle consistent with the acute angle a of the dust discharge tube.

[0087] The non-vacuum sander, the central vacuum sander 10 and theself-generated vacuum sander 150 utilize a 150 watt power air motorwhich operates from a source providing 6.1 bar air pressure and the airmotor is capable of providing up to 10,000 revolutions per minute.

[0088] It is to be especially noted that the foregoing discusseddimensions are intended to preferably apply to the three types of randomorbital sanders discussed above relative to FIGS. 1-21, and while thedimensions of the air motor are preferably incorporated in the orbitalsander of FIGS. 22 et seq., the other dimensions listed in the abovetable relating to the angles and dimensions of the hose connections areoptional. It will also be appreciated that the connections between thehousing and the pad of the orbital sander shown in FIGS. 22 et seq. maybe used independently with other types of motors, and that suchconnections are not restricted to the use with an air motor having thedimensions discussed above.

[0089] In accordance with another aspect of the present invention, thebearings 276 (FIG. 23), which are analogous to the bearings 55 (FIGS. 1Aand 17), are supplied with compressed air and a one-way valve whichprevents foreign matter from effectively entering the eccentric housing57 in which they are located. In this respect, it is to be noted fromFIGS. 1A, 1B, 1C, 1D and 1F that compressed air is conducted from bore38 (FIGS. 1A and 1F) through bore 134 and into bore 134′. The compressedair then passes into groove 136 (FIG. 1D) in cylinder surface 50 and acounterpart groove (not shown) in cylinder surface 35. The compressedair then passes through groove 140′ (FIG. 1B) in surface 64 of plate 32from groove 136, and it also passes through groove 141′ (FIG. 1C) fromthe counterpart (not shown) of groove 136. As expressed above, thecompressed air emanating from grooves 140′ and 141′ enter the radialslots 139′ (FIG. 1D) of the rotor 25 to force vanes 136′ outwardly.

[0090] There is a working clearance between the parts of air motorconsisting of cylinder 24 and rotor 25 and plates 32 and 33. Thus thecompressed air from grooves 140′ and 141′ will pass between plate 32 androtor 25 and will also pass between plate 33 and rotor 25. Thiscompressed air will then enter rotor keyway slot 180 (FIGS. 1A, 1D and1F), and then pass around key 181 which is located in key slot 182 inshaft 27.

[0091] In accordance with one embodiment of the present invention, theshaft 27 of the air motor has been modified to be shaft 27′ shown inFIGS. 17 and 18. In this respect, a cross bore 183 has been drilled inshaft 27′, and a coaxial duct in the form of a bore 184 has been drilledin the lower part of shaft 27′ in communication with bore 183, and acounterbore 185 has been drilled in the lower end of bore 184.Counterbore 185 is in communication with the chamber 187 of eccentrichousing 57 in which bearings 55 are located. As can be seen from FIGS.1A and 17, there is a small space 189 in chamber 187 above the uppermostbearing 55. A filter disc 188, which is fabricated of spunbondedpolyester, and a duckbill one-way valve 190 are located in counterbore185 and retained therein by retaining sleeve 191 which is press-fittedinto counterbore 185 and bears against the enlarged annular portion 186of valve 190. The filter 188 filters the compressed air passing throughthe duckbill valve. As shown in FIG. 18, there is a spacer 192 betweenbearings 55, and there is a spacer 193 between lower bearing 55 andBelleville washer 58. Spacers 192 and 193 are thin annular metal discswhich fit on stub shaft 53, and their outer diameters bear on the innerraces of bearing 55 without obstructing the spaces between the inner andouter races. The upper spacer 192 spaces the two bearings 55 so thattheir outer races do not contact each other. The lower spacer 193 alsofunctions somewhat as a labyrinth seal to create a tortuous path back tothe lower bearing 55 when air tends to suck upwardly into the lowerbearing 55 when the motor stops. The foregoing structure thus causes airflow into chamber 187 and through bearings 55 and through the annularspace 196 between Belleville washer 58 and portion 195 of stub shaft orspindle 53 into the space above sanding disc 14. This pressure is morepositive than the pressure outside of eccentric housing 57, therebypreventing sanding dust and other foreign materials from enteringbearings 55 in chamber 187 from the area above pad 14. It is to be notedthat since duckbill valve 190 is a one-way valve, the air in chamber 187cannot be drawn back into bore 184 when the air motor inherentlyfunctions as a pump when the compressed air flow thereto is terminated,thereby obviating the induction of foreign material laden air intochamber 187.

[0092] In FIG. 19 another embodiment of the present invention isdisclosed. All parts which are identical to the numerals in FIG. 1Arepresent identical elements of structure. In FIG. 19 motor shaft 27 hasbeen modified by creating a duct in the form of a bore 200 therein whichextends from the top of shaft 27 to counterbore 201 which is incommunication with space 189 within eccentric housing chamber 187. Aduckbill valve 202 is located in counterbore 201 and is retained thereinby press-fitted sleeve 203, as in the embodiment of FIGS. 17 and 18. Afilter 204 which is of the same type described above and designated 188is located above valve 202 within counterbore 201.

[0093] Bore 200 receives its air from clearance space 61. In thisrespect, there is leakage between shaft 27 and plate 32, and this airalso passes through upper bearing 29 to effect cooling thereof andthereafter it passes into clearance space 61 from which it passes intothe top of bore 200 which leads to filter 204 and duckbill valve 202.The air emanating from duckbill valve 202 functions in the same manneras described above relative to duckbill valve 190 of FIGS. 17 and 18.

[0094] It is to be especially noted that in the embodiments of FIGS. 17,18 and 19, the only modification has been to the existing shaft of therandom orbital tool, and that there has been no requirement for anyducts in the cylinder 24 in which rotor 25 rotates.

[0095] Another way of conducting compressed air to bore 200 in FIG. 19is to drill a small hole (not shown) in upper plate 32 so thatcompressed air will pass through this hole, through bearing 29 (FIG. 1A)and through space 61 into duct or bore 200. This hole may receive itsair from duct 140′ (FIG. 1B) or from the clearance between planarsurface 34 of plate 32 and cylinder 24. Also, the hole in plate 32 neednot be directed to bearing 29, but may be positioned to communicate withclearance space 61 through the clearance between the planar surface 34of plate 32 and cylinder 24 and through annular portion 63 (FIG. 1B) ofplate 32. Also bore 200 may obtain compressed air because of leakagearound the outer circumferential edge 43 of plate 32 into clearancespace 61.

[0096] Still another way of providing compressed air to bearing chamber187 is shown in FIG. 20, and it would be to form a duct in the form of aslot 211 on the outside of the portion of shaft 27 which is abreast ofbearing 30 and drill a hole 212 in line with slot 211 through the top ofhousing 57 into chamber 187. Slot 211 would have its open side coveredby the contiguous inner race of bearing 30. Compressed air could thuspass from clearance space 213 into bearing chamber 187, the clearancespace 213 receiving its compressed air through the clearance between theundersurface of rotor 25 and the planar upper surface of plate 33 andthrough keyway 180. In this embodiment the compressed air does not passthrough a duckbill valve and filter.

[0097] Another way of conducting compressed air to chamber 187 is shownin FIG. 21 wherein an inclined duct or bore 214 is drilled through theportion of shaft 27 abreast of bearing 30 and duct 214 is incommunication with a counterbore (not numbered) housing a filter andduckbill valve, such as shown and described in FIGS. 17-19 so that thereis communication between clearance space 213 and small space 189 inchamber 187 through the filter and duckbill valve.

[0098] It will be appreciated that the various clearances referred toabove through which compressed air passes are considered to be ductswithin the housing through which compressed air is conducted to bearingchamber 187.

[0099] In FIGS. 22-31 the improved orbital sander 220 of the presentinvention is shown. Orbital sander 220 is of the same general type shownin FIG. 4, namely, a non-vacuum type of sander which does not have anyvacuum associated with it for the purpose of conveying an abrasive dustwhich is generated during a sanding operation. However, it will beappreciated that it may be of the other types noted above, namely, thecentral vacuum type which has a vacuum hose attached at one end to acentral vacuum source or the type which is a self-generated vacuum typewherein the exhaust air from the air motor is associated with anaspirator in communication with the shroud for carrying the weighteddust which is generated during a sanding operation.

[0100] The orbital sander 220 includes an upper housing section 221having an integral air inlet duct 222. Lever 223 is pivotally mounted onpin 224 and it functions in the same manner described above relative toFIG. 11, or it can function in any other suitable way known in the artto control the flow of air to compressed air motor 225 which may beidentical in all respects to that shown above in FIGS. 1A through 1Fexcept that the shaft 227 is of a different configuration as are theeccentric housing 229 and the counterweights 230 and 231. The housinggrip 232 of rubber-type material is mounted on housing section 221.

[0101] A pad 233 is secured to pad backing plate 234 by a plurality ofscrews 235 (FIG. 25) which extend through openings, such as 237 in pad233, and through openings 239 in pad backing plate 234 and are receivedin nuts 240 which are molded integrally into the bases or lower barmembers 241 of columnar units 242 each having a row of a plurality ofspaced plastic columns 243 molded integrally therewith, with saidcolumns 243 being molded integrally with upper bar member 244. Each bar244 includes nuts 245 molded therein. While the columns 243 of each roware shown in alignment, it will be appreciated that they may bestaggered or offset. The columns are of tapered circular cross sectionthroughout and have the dimensions shown in FIG. 29A with their smallestdimension at each midpoint, which is the most flexible part of eachcolumn. In other words, the columns flare outwardly from positionssubstantially at their midpoints. I will be appreciated that the columnsmay be of other cross sectional shapes, such as cylindrical, and thatsuch shapes could function, but they would not function in the samemanner as the specific shape show. It will also be appreciated that thesmallest cross sectional dimension of each column need not be locatedsubstantially at its midpoint, but can be placed anywhere between itsends. Also, it will be appreciated that there can be more than onereduced cross sectional area in each column. The preferred shape anddimensions of the columns 243 are shown in millimeters in FIG. 29A,along with the height dimension of the columnar unit 241.

[0102] In its more specific aspects, the base 241 of each columnar unit242 includes an embedded metal plate 247 (FIGS. 29 and 30). Theconfiguration of metal plate 247 is such that it has apertures 249therein through which the molded plastic of base 241 extends. Thus,plates 249 rigidize bases 241. Also, the nuts 235, in addition to beingmolded into bases 241, are also set into plates 247. Thus, each base 241is essentially reinforced plastic which provides great rigidity.

[0103] Each upper bar member 244 also includes a metal plate 250confined fully within upper bar member 244. Metal plate 250 includes aplurality of apertures 251 similar to apertures 249 of lower bar member241 through which the molded plastic of header 242 extends. Nuts 245, asnoted above, are molded into each upper bar member 244, and these nutsalso are in abutting relationship to each apertured plate 250.

[0104] The plastic of column assemblies 241 is molded polyester and isgrade “High Performance” and can be commercially obtained from DuPontEngineering Polymers Company under the trademark HYTREL and is furtheridentified by number 5546. This plastic provides good columnar strengthwhile permitting good lateral flexibility so that the pad 233 secured tolower bar members 241 of columnar units 242 will have a good orbitalmotion while the plastic columns 243 provide good columnar strength. Theoutside height dimension across bar members 241 and 244 is 27.85millimeters before it is mounted (FIG. 29A). It will be appreciated thatother suitable plastics may be used.

[0105] The columnar units 242 are secured to housing sections 253 byscrews 254 which extend through suitable apertures 255 in housingsections 253 and are received in nuts 245. The upper bar members 244 ofcolumnar units 242 fit into recesses 257 of identical housing sections253.

[0106] Identical housing sections 253 are secured to upper housingsection 221 in the following manner. Housing section 221 is identical tohousing section 22 of FIGS. 2 and 1A. In this respect, housing section221 includes an annular groove 259 (FIG. 23) which receives ridge 260 ofeach identical lower housing section 253. A ridge 261 (FIG. 23) isreceived in groove 262 of lower housing sections 253. Ridge 261 of upperhousing section 221 is of complementary mating relationship to groove262 in that it is interrupted to receive the ridge configurations 263and 264 of upper housing sections 253 which act as keys to preventrelative rotation between upper housing section 221 and lower housingsection 253. Any other suitable connection between the upper housingsection 221 and lower housing sections 253 can be used.

[0107] The lower housing sections 253 are secured to each other and toupper housing section 221 by nut and bolt assemblies. In this respect,bolts 265 extend through bores 267 in lower housing sections 253 and areretained therein by nuts 269 such that lower housing sections 253 assumean end-to-end abutting relationship such as shown in FIGS. 22 and 27along seam 270.

[0108] By virtue of the above-discussed construction, upper housingsection 221 is firmly attached to lower housing section 253. The upperbar members 244 of columnar units 242 are firmly secured to lowerhousing sections 253, and the pad plate 234 is firmly secured to lowerbar members 241 of columnar units 242. There is a space 271 (FIG. 28)between the lower edges of lower housing sections 253 and the uppersurface 272 of pad plate 234. Thus, the only contact between pad plate234 and lower housing sections 253 is through columnar units 242. Asnoted above, upper bar members 244 are firmly attached to lower housingsections 253 and lower bar members 241 of columnar units 242 are firmlyattached to pad plate 234. Thus, the only connection between lowerhousing sections 253 and pad plate 234 which can yield are plasticcolumns 243 which extend between lower bar members 241 and upper barmembers 244 of columnar units 242.

[0109] The overall height of the orbital sander along its verticalcenterline from the top of housing grip 232 to the underside of pad 233is 98.33 millimeters. However, it will be appreciated that thisdimension may be varied for other constructions of orbital sanders.Also, as noted above, the columnar units 242 need not be used with thespecific low-height compressed air motor described above, but may beused with other types of motors.

[0110] The oscillatory motion of pad 233 is produced in the followingmanner. A bolt 273 extends through aperture 274 in pad plate 234 and isthreadably received in spindle 275 which is retained with a press-fit inthe inner races of the bearings 276 which are located in eccentrichousing 229. A pin 279 (FIG. 23), which is fixedly mounted in bore 281in spindle 271, extends through a bore 280 in pad plate 234 to preventrotation of pad plate 234 as it is secured to spindle 275 by bolt 273during assembly, and it also provides an orbital driving connection tothe pad during sander operation. In the latter respect, as motor shaft282 rotates, pin 281, bolt 273, and bearings 276 will be driveneccentrically relative to the axis of shaft 281 and thus pad plate 234and pad 233 will be driven in an orbital motion. The foregoingconnection is conventional in the art.

[0111] It can be seen from FIG. 23 that columns 243 are distorted andnot perfectly symmetrical as shown in FIG. 28. This is due to the factthat when the pin 279 and bolt 273 secure the pad plate 234 to spindle275, columns 243 will always be distorted. The reason they are perfectlysymmetrical in FIG. 28 is because they are not shown in the positionthey assume when the pad plate 234 is connected to the spindle by bolt273 and pin 279.

[0112] In FIG. 23 a duct arrangement is shown in shaft 282 forconducting compressed air to chamber 278 of eccentric housing 229. Thisduct arrangement may be identical to that described above relative toFIGS. 17-19 and may function in the same manner. Also, the arrangementfor conducting compressed air to chamber 278 of eccentric housing 229may also be the same as described above relative to FIGS. 20 and 21 andalso as described above without being illustrated.

[0113] Conventional clips 290, which are well known in the art, aremounted at opposite ends of pad plate 272 for securing opposite ends ofthe sanding paper which extends across the pad 233.

[0114] While preferred embodiments of the present invention have beendisclosed, it will be appreciated that it is not limited thereto but maybe otherwise embodied within the scope of the following claims.

1. An orbital sander comprising a housing, a compressed air motor insaid housing, a pad support secured to said motor, and first and secondelongated rows of spaced plastic columns located on opposite sides ofsaid motor and located between said housing and said pad support.
 2. Anorbital sander as set forth in claim 1 wherein said first and secondrows of spaced plastic columns have lower ends proximate said padsupport and have higher ends proximate said housing, and wherein a firstbar member is located at each of said lower ends of said first andsecond rows of plastic columns, and wherein a second bar member islocated at each of said upper ends of said first and second rows ofplastic columns.
 3. An orbital sander as set forth in claim 2 includingfirst fasteners securing said pad support to said first bar members, andsecond fasteners fastening said housing to said second bar members. 4.An orbital sander as set forth in claim 2 wherein said first and secondbar members are molded integrally with each said first and second rowsof spaced plastic columns.
 5. An orbital sander as set forth in claim 2wherein said columns have at least one reduced cross sectional areabetween their ends.
 6. An orbital sander as set forth in claim 5 whereinsaid columns are of substantially circular cross section.
 7. An orbitalsander as set forth in claim 1 including a shaft in said motor, a rotormounted on said shaft, a compressed air duct in said motor forconducting compressed air to said rotor, an eccentric housing mounted onsaid shaft, a chamber in said eccentric housing, at least one bearing insaid eccentric housing, and said pad support being secured to saideccentric housing, said first and second rows of spaced plastic columnshaving lower ends proximate said pad support and have higher endsproximate said housing, and wherein first bar members are located atsaid lower ends of each of said first and second rows of plasticcolumns, and wherein second bar members are located at said upper endsof each of said first and second rows of plastic columns.
 8. An orbitalsander as set forth in claim 7 including first fasteners securing saidpad support to said first bar members, and second fasteners fasteningsaid housing to said second bar members.
 9. An orbital sander as setforth in claim 7 wherein said first and second bar members are moldedintegrally with each said first and second rows of spaced columns. 10.An orbital sander as set forth in claim 9 wherein said columns have atleast one reduced cross sectional area between their ends.
 11. Anorbital sander as set forth in claim 7 including means in said motor forconducting compressed air to said chamber.
 12. An orbital sander as setforth in claim 7 including another duct in said shaft in communicationwith said compressed air duct and said chamber for conducting compressedair to said chamber.
 13. An orbital sander as set forth in claim 12including a one-way valve in said another duct for permitting flow onlyto said chamber.
 14. An orbital sander as set forth in claim 13including a filter in said another duct.
 15. An orbital sander as setforth in claim 12 wherein said another duct is a bore in said shaft, andincluding a keyway in said rotor, a key slot in said shaft, a key insaid key slot and extending into said keyway, a clearance between saidkey and said key slot, a crossbore in said shaft in communication withsaid key slot, and said crossbore being in communication with said borein said shaft.
 16. An orbital sander as set forth in claim 15 includinga pad connected to said eccentric housing, a face on said pad support onthe opposite side thereof from said eccentric housing, and wherein saidorbital sander has a vertical centerline, and wherein said orbitalsander has a height dimension from the top of its housing to said faceof said pad which is not greater than about 98 millimeters.
 17. Anorbital sander as set forth in claim 15 including a counterbore in saidbore in communication with said chamber, and a one-way valve in saidcounterbore.
 18. An orbital sander as set forth in claim 17 including afilter in said counterbore.
 19. An orbital sander as set forth in claim18 wherein said one-way valve is positioned between said filter and saidchamber.
 20. An orbital sander as set forth in claim 7 including anupper plate in said housing, an upper bearing in said upper platesupporting said shaft, a first clearance between said upper plate andsaid shaft, a second clearance between said shaft and said housing, andsaid another duct in said shaft being in communication with said firstclearance through said upper bearing and said second clearance.
 21. Anorbital sander as set forth in claim 20 including a pad connected tosaid eccentric housing, a face on said pad support on the opposite sidethereof from said eccentric housing, and wherein said orbital sander hasa vertical centerline, and wherein said orbital sander has a heightdimension from the top of its housing to said face of said pad which isnot greater than about 98 millimeters.
 22. An orbital sander as setforth in claim 20 wherein said another duct is a bore in said shaft, andincluding a counterbore in said bore in communication with said chamber,and a one-way valve in said counterbore.
 23. An orbital sander as setforth in claim 22 including a filter in said counterbore.
 24. An orbitalsander as set forth in claim 23 wherein said one-way valve is positionedbetween said filter and said chamber.
 25. An orbital sander as set forthin claim 7 including a pad connected to said eccentric housing, a faceon said pad support on the opposite side thereof from said eccentrichousing, and wherein said orbital sander has a vertical centerline, andwherein said orbital sander has a height dimension from the top of itshousing to said face of said pad which is not greater than about 98millimeters.
 26. An orbital sander as set forth in claim 7 wherein saidanother duct is a slot in the outside of said shaft.
 27. An orbitalsander as set forth in claim 26 including a second bearing mounting saidshaft, and wherein said slot is located adjacent said second bearing.28. An orbital sander as set forth in claim 7 wherein said another ductis an inclined bore in said shaft.
 29. An orbital sander as set forth inclaim 7 including means in said motor for conducting compressed air tosaid chamber, and wherein said first and second bar members are moldedintegrally with each said first and second rows of spaced columns, andwherein said columns have at least one reduced cross sectional areabetween their ends.
 30. An orbital sander as set forth in claim 29wherein said columns are of substantially circular cross section.
 31. Aplastic columnar unit for an orbital sander comprising an upper barmember, a lower bar member, and a row of a plurality of spaced columnsbetween said upper and lower bar members.
 32. A plastic columnar unit asset forth in claim 31 wherein said spaced columns are molded integrallywith said upper and lower bar members.
 33. A plastic columnar unit asset forth in claim 32 including metal plates in said upper and lower barmembers.
 34. A plastic columnar unit as set forth in claim 33 includingfasteners molded in said upper and lower bar members.
 35. A plasticcolumnar unit as set forth in claim 31 wherein said columns have atleast one reduced cross sectional area between their ends.
 36. A plasticcolumnar unit as set forth in claim 35 wherein said spaced columns aremolded integrally with said upper and lower bar members.
 37. A plasticcolumnar unit as set forth in claim 36 including metal plates in saidupper and lower bar members.